Tuesday, October 21, 2014

Would Life Evolve the Same Way If the World Started Over?

By Emily Singer, Quanta Magazine

In his fourth-floor lab at Harvard
University, Michael Desai has created hundreds of identical worlds in
order to watch evolution at work. Each of his meticulously controlled
environments is home to a separate strain of baker’s yeast. Every 12
hours, Desai’s robot assistants pluck out the fastest-growing yeast in
each world — selecting the fittest to live on — and discard the rest.
Desai then monitors the strains as they evolve over the course of 500
generations. His experiment, which other scientists say is unprecedented
in scale, seeks to gain insight into a question that has long bedeviled biologists: If we could start the world over again, would life evolve the same way?

Many biologists argue that it would not, that chance mutations early
in the evolutionary journey of a species will profoundly influence its
fate. “If you replay the tape of life, you might have one initial
mutation that takes you in a totally different direction,” Desai said,
paraphrasing an idea first put forth by the biologist Stephen Jay Gould
in the 1980s.
Desai’s yeast cells call this belief into question. According to results published

in Science in June, all of Desai’s yeast varieties arrived at
roughly the same evolutionary endpoint (as measured by their ability to
grow under specific lab conditions) regardless of which precise genetic
path each strain took. It’s as if 100 New York City taxis agreed to take
separate highways in a race to the Pacific Ocean, and 50 hours later
they all converged at the Santa Monica pier.

The findings also suggest a disconnect between evolution at the
genetic level and at the level of the whole organism. Genetic mutations
occur mostly at random, yet the sum of these aimless changes somehow
creates a predictable pattern. The distinction could prove valuable, as
much genetics research has focused on the impact of mutations in
individual genes. For example, researchers often ask how a single
mutation might affect a microbe’s tolerance for toxins, or a human’s
risk for a disease. But if Desai’s findings hold true in other
organisms, they could suggest that it’s equally important to examine how
large numbers of individual genetic changes work in concert over time.

“There’s
a kind of tension in evolutionary biology between thinking about
individual genes and the potential for evolution to change the whole
organism,” said Michael Travisano,
a biologist at the University of Minnesota. “All of biology has been
focused on the importance of individual genes for the last 30 years, but
the big take-home message of this study is that’s not necessarily
important.Continue Reading...